1. Field of the Invention
The present invention relates to a discharge valve assembly of a reciprocating compressor, and particularly, to a discharge valve assembly of a reciprocating compressor capable of minimizing noise generation and the amount of contact impact.
2. Description of the Background Art
In general, a reciprocating compressor is an apparatus that sucks and compresses a refrigerant gas as a piston linearly reciprocates in a cylinder. Such a reciprocating compressor is divided into two types according to the driving mechanism. Of the two types, one is that a rotating movement of a motor is converted into a linear reciprocation and the linear reciprocation is transferred to the piston, and the other one is that a linear reciprocation of the motor is directly transferred to the piston.
FIGS. 1 shows one example of a reciprocating compressor which is operated in such a manner that a linear reciprocation of a motor is directly transferred to a piston. As shown, the reciprocating compressor comprises: a casing 10 coupled to a gas suction pipe 1 and a gas discharge pipe 2; a front frame 20 and a middle frame 30 installed in the casing 10 at a predetermined distance therebetween and elastically supported; a driving motor 40 mounted between the front frame 20 and the middle frame 30, for generating a linearly reciprocating driving force; a cylinder 50 inserted in the first frame 20; a piston 60 linearly reciprocating in the cylinder 50 upon receiving a driving force of the driving motor 40; a rear frame 70 for covering the piston 60; a resonant spring 80 for elastically supporting the piston 60 to thereby induce resonance; a suction valve 90 coupled to a front end surface of the piston 60, for controlling the flow of a gas which is introduced into the cylinder 50 by the linear reciprocation of the piston 60; and a discharge valve assembly 100 installed at one side of the cylinder 50, for controlling discharging of a compressed gas which is compressed in the cylinder by the linear reciprocation of the piston 60.
The driving motor 40 includes: an outer stator 41 mounted between the front frame 20 and the middle frame 30; an inner stator 42 inserted in the outer stator 41 and mounted at the front frame 20; a winding coil 43 coupled to the outer stator 41; and a mover 44 installed between the outer stator 41 and the inner stator 42 to be linearly movable. The mover 44 includes a cylindrical holder 45 and a plurality of magnets 46 coupled to the holder 45, and the holder 45 is connected to the piston 60.
The discharge valve assembly 100 includes a discharge cover 101 for covering an inner space of the cylinder 50; a discharge valve 102 positioned in the discharge cover 101, for opening or closing the inner space of the cylinder; and a spring 103 for elastically supporting the discharge valve 102. The gas discharge pipe 2 is connected to the discharge cover 101.
Undescribed reference mark 104 is a coupling bolt, and 105 is a nut.
The operation of the reciprocating compressor having such a structure will now be described.
First, when power is applied to the compressor, a linearly reciprocating driving force is generated at the driving motor 40. Thus, the mover 44 of the driving motor linearly reciprocates, and a linearly reciprocating driving force of the mover 44 is transferred to the piston 60, so that the piston 60 linearly reciprocates in the inner space of the cylinder 50. By a pressure difference generated in the cylinder 50 due to a linear reciprocation of the piston 60 in the inner space of the cylinder 50, the suction valve 90 and the discharge valve assembly 100 open or close a gas passage, whereby a gas is sucked into, compressed in and discharged from the cylinder 50. The compressed gas discharged from the inner space of the cylinder 50 passes the inside of the discharge cover 101 and then is discharged through the gas discharge pipe 2. Such processes are continuously repeated to compress a gas.
Meanwhile, in the reciprocating compressor, the discharge valve assembly 100 for discharging a compressed gas according to a linear reciprocation of the piston 50 affects how much noise is generated. Also, the operation of the discharge valve assembly 100 affects flow resistance of a discharged gas, thereby affecting the amount of the discharged gas. Accordingly, researches on the discharge valve assembly 100 are very important in improving reliability and efficiency, and thus the researches thereon are actively ongoing.
FIG. 2 shows one example of a conventional structure of a discharge valve assembly of the reciprocating compressor. As shown, the discharge valve assembly 100 of the conventional compressor comprises: a discharge cover 101 for covering an inner space of the cylinder 50; a discharge valve 102 inserted in the discharge cover 101, for opening or closing the inner space of the cylinder 50; and a valve spring 103 for elastically supporting the discharge valve 102, wherein the discharge cover 101 is formed as a cap shape with a certain thickness. Namely, as for the discharge cover 101, a fixing portion 112 is bent and extends from one side of a cylindrical portion 111 having certain length and outer diameter, and is coupled to the front frame 20, and a discharge opening 113 to which the gas discharge pipe 2 is connected is formed at one side of the cylindrical portion 111.
The discharge valve 102 is formed as a circular compression plane 123 whose one side is coupled to a spring and whose other side blocks the inner space of the cylinder 50.
The valve spring 103 is a coil spring having a certain length.
One side of the valve spring 103 is coupled to the discharge valve, and its other side contacts with and is supported by an inner surface of the discharge cover. At this time, the compression plane 123 of the discharge valve comes in contact with a contact surface (S1), an end surface of the cylinder 50. And an inner surface of the discharge cover, which is in contact with the valve spring 103, is a plane parallel to the contact surface (S1) of the cylinder 50, which comes in contact with the compression plane 123 of the discharge valve.
The operation of the discharge valve assembly of the conventional reciprocating compressor having such a structure will now be described in detail.
First, when the piston 60 moves from a top dead point to a bottom dead point, the compression plane 123 of the discharge valve adheres to the contact surface (S1) of the cylinder 50 by a pressure difference of the inner space of the cylinder 50, and simultaneously, the suction valve 90 is opened, allowing a gas to be introduced into the inner space of the cylinder 50 through a passage formed in the piston 60.
And, when the piston 60 moves from a bottom dead point to a top dead point, the suction valve 90 blocks a gas passage of the piston 60, thereby gradually compressing the gas sucked in the inner space of the cylinder 50. When the gas reaches a set compression state, the discharge valve 102 supported by the valve spring 103 is opened, thereby discharging a compressed gas. By continuously repeating such processes, the gas is compressed.
In the discharge valve assembly having such a structure, a section of the inner space of the cylinder where a gas is compressed is a circular shape, and the discharge valve 102 for opening or closing the inner space is formed as a circular shape. Thus, the inner space of the cylinder 50 and the discharge valve 102 for opening or closing the inner space have the shapes which can allow a maximum discharge area. Therefore, the flow of a discharged gas is smooth, and a large amount of discharge gas is discharged at a time, thereby improving efficiency.
However, the discharge valve assembly having such a structure has the following problems. In order to make a movement of the discharge valve 102 smooth, stiffness of the valve spring 103 which elastically supports the discharge valve 102 is low. For this reason, when the discharge valve 102 moves, a range of the movement becomes wide, thereby increasing the amount of impact generated by contact with the cylinder 50. Accordingly, a valve contact noise of high frequency is greatly generated.
In addition, the discharge valve is opened when a force due to pressure of a compression space formed by the piston and the discharge valve is greater than the sum of an adhesive force of oil at the contact surface, a force due to a valve spring and a force due to pressure in the discharge cover. This makes the piston unnecessarily work on a fluid, thereby resulting in overcompression-related loss.